Phenylephrine

General

• Type: Vasopressors
• Dosage Forms:
• Common Trade Names: Neosynephrine

Adult Dosing

Hypotension

• Start 100-200 mcg/min then taper down
  • 40-60 mcg/min works for most

Low Flow Priapism

• Dilute phenylephrine 1mg in 9mL NS for final concentration of 100mcg/mL
  • For 500 mcg/ml, take 0.5 ml of 10mg/ml phenylephrine, and dilute in 9.5 cc NS
• Inject base of penis with 29-Ga needle (after blood aspiration to confirm position)
  • 100-500 mcg every 3-5min (max 1000 mcg) until resolution or 1 hour

Special Populations

• Pregnancy Rating: C
• Lactation: infant risk cannot be ruled out
• Renal Dosing
  • Adult
  • Pediatric
• Hepatic Dosing
  • Adult
  • Pediatric

Contraindications

• Allergy to class/drug

Adverse Reactions

• Baroreceptor-mediated reflex bradycardia
• If extravasates use phentolamine

Pharmacology

• Half-life:
• Metabolism:
• Excretion:
• Mechanism of Action: selective α₁ agonist causes vasoconstriction

Primary Receptor

• α₁

Relative Effects

• ↑SVR
• ↓HR (reflex bradycardia)

Notes

• Use with caution in patients with spinal cord injury-related bradycardia
• Useful for treatment of vasodilatory shock when norepinephrine or dopamine have precipitated tachyarrhythmias
• In patients with ↓LV function, unopposed α₁ may lead to decreased CO or myocardial ischemia
  • However clinical trials do not support these effects when used in clinically appropriate dose range

Indication

• Neurogenic Shock
• Second line agent for septic shock

See Also

http://www.atsjournals.org/doi/abs/10.1164/rccm.201006-0972CI?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed#readcube-epdf